1. Field of the Invention
This invention relates to airspeed sensing systems.
2. Description of the Prior Art
The airspeed sensing systems currently used on fixed-wing aircraft commonly comprise a pitot tube and a pressure transducer arrangement which provides analog electrical signals representing the pitot pressure and the static pressure. Corrections are applied to these signals in dependence on the air temperature, and the true airspeed can be computed using a formula of the type: EQU T.A.S.=fn(P-S).multidot.fn(S).multidot.fn.multidot.(.theta.m)
where
T.A.S. is the true airspeed PA1 P is the pitot pressure PA1 S is the static pressure .theta. m is the measured outside air temperature.
An alternative approach is to use a venturi and to measure the pressure differential which it creates.
There are several problems with such airspeed sensing systems. Thus, for example, care has to be taken to mount them on the aircraft at a position which is exposed to a representative and reasonably non-turbulent airflow. These problems become even more serious in the cases of helicopters, vertical take-off and landing (VTOL) aircraft and hovercraft. In the case of helicopters, for example, the rotor blades have a very substantial effect on the air flow around the fuselage and in fact cause a downwash effect with resultant pulsating pressure changes.